High protein nutritive foods are useful for patients who need to ingest large amounts of proteins, such as those with liver diseases, nephrosis syndrome, gastric ulcer, duodenal ulcer or the like and postoperative patients. They are also well suited as dietary foods for healthy persons.
Such high protein nutritive foods include powdery or granular soybean protein which is well known. Such soybean protein is very difficult to eat and is therefore usually prepared and taken in the form of a liquid as dissolved in water, milk or the like, but the liquid product has the drawback of being very disagreeable to the taste and difficult to drink. Further in recent years, various foods of low calorific value resembling snack cakes have been developed as dietary foods, and some of them have been made commercially available, whereas they in no way taste agreeable or feel satisfactory to eat in respect of feeling of eating (or texture) such as feel to the tooth, mouthfeel, melting in the mouth, etc. For example, Examined Japanese Patent Publication SHO 59-15615 discloses a process for preparing a high protein snacklike food by adding an alkali solution to casein to obtain dough with a water content of about 13 to about 18%, and extruding the dough at a high temperature and high pressure into an atmosphere with room temperature and ordinary pressure to expand the dough. However, the product obtained by this process inevitably has a high water content of about 7 to about 10 wt. %, such that even if giving a crisp texture to some extent, the product fails to give a short and light texture and is not meltable smoothly in the mouth like potato chips. Further Examined Japanese Patent Publication SHO 62-12972 discloses a high protein snack food obtained by extruding soybean protein powder with addition of water, heating the extrudate in water, thereafter mixing the extrudate with soybean protein powder and freeze-drying the mixture. With this process, the extrudate is mixed with soybean protein and freeze-dried, so that the product feels hard and munching like dried soybean curd before reconstitution with water, gives a poor mouthfeel, is not soluble smoothly in the mouth and is therefore in no way satisfactory to eat.